1. Field of the Invention
The invention relates to an optical filter such as a parallax barrier, which forms light shielding barrier on a transparent substrate, and also relates to a stereoscopic visual display device and to a multiple visual display device, which use the optical filter.
2. Description of Related Art
The technology of optical filtering for example by a parallax barrier that forms a light shield (also referred to here as just “barrier”) on a transparent substrate made of transparent glass or transparent resin is known for stereoscopic visual display devices without wearing special glasses. Also known are multiple image display devices that provide different images simultaneously to more than two viewers.
FIG. 1 shows an exemplary parallax barrier. As seen in this figure, parallax barrier 100 comprises an opening (slit) area 103 that lets light penetrate, on glass substrate 101 where barrier 102 is formed, which blocks light penetration.
FIG. 2A is a simple diagram showing the principle of a stereoscopic visual display device that does not require wearing special glasses of two viewpoints with parallax barrier 100. As seen here, left-eye image L and right-eye image R are displayed in alternate shifts on liquid crystal display device 104. Black matrix B is positioned between a left-eye image L and a right-eye image R, which partitions the left-eye image L and the right-eye image R. Each interval of the left-eye image L and the right-eye image R is varied in the manufacturing process. The intervals are arranged to specified precise values, called “pixel pitch”. FIG. 2A shows a pixel pitch as P.
In FIG. 2A, a left-eye image L and a right-eye image R on liquid crystal display device 104 traverse opening area 103 of parallax barrier 100 as a pair. The left-eye image L and the right-eye image R respectively lead to a viewer A's left and right eyes. As a result, viewer A can achieve stereoscopic vision using binocular parallax.
FIG. 2A also shows a diagram of the stereoscopic visual display device from a top-down perspective. Here, the left-eye image L and the right-eye image R, which are displayed to opening (slit) area 103 and liquid crystal display device 104, are formed in vertical stripes, i.e. in a top-down direction. Additionally, FIG. 2A shows a stereoscopic visual display device from two views, although stereoscopic visual display devices of three or more viewpoints are contemplated.
FIG. 2B is a simple diagram that shows the principle of a device having multiple visual displays, via use of parallax barrier 100. Here, image V1 for viewer B and image V2 for viewer C are displayed in alternate shifts on liquid crystal display 105. A black matrix is positioned between image V1 for viewer B and image V2 for viewer C, thus constituting a partition with image V1 for viewer B and image V2 for viewer C. Although each interval of image V1 for viewer B and image V2 for viewer C is varied in the manufacturing process, the interval may be set to a precise pixel pitch P.
In FIG. 2B, image V1 for viewer B and image V2 for viewer C on liquid crystal display 105 traverse opening area 103 of parallax barrier 100 as a pair. Image V1 for viewer B and image V2 for viewer C respectively lead to viewer B and viewer C. As a result, each of viewers B and C can observe different images.
FIG. 2B also shows a diagram of a multiple visual display device from a top perspective. Here, image V1 for viewer B and image V2 for viewer C, which are displayed through opening (slit) area 103 and liquid crystal display device 105, form in vertical stripes (top-down direction). In addition, FIG. 2B shows a multiple visual display device that displays two images, although multiple visual display devices that display three or more images are contemplated.
As shown in this figure with parallax barrier 100, the distances between the centerline of each adjoining slit, (opening area pitch, which is described as slit pitch below), are formed to meet certain criteria that allow a viewer A to experience stereoscopic vision without a sense of incongruity as in FIG. 2A. The criteria also provide the condition wherein viewer B and viewer C can observe different images without the sense of incongruity as in FIG. 2B.
Specifically, (see FIG. 2A), determining a distance between a viewer A's eyes as E, a pixel pitch of liquid crystal display device 104 as P, and a split pitch of parallax barrier as S, an ideal slit pitch can be calculated by the following expression (equation 1).S=2×P×E/(P+E)  (equation 1)
Here, 65 mm is generally considered ideal for the distance between human's eyes. For example, assuming slit pitch of liquid crystal display 104 is P=0.11 mm, approximately S=0.219628 mm is obtained from equation 1.
Thus, in order for a viewer to watch a stereoscopic image without a sense of incongruity, it is necessary for a slit to form a parallax barrier so that all slit pitches become S=0.219628 nm.
In addition, as shown in FIG. 2B, it is necessary for a slit to form an arranged parallax barrier so that the slit pitch allows viewers B and C to watch different images without the sense of incongruity. However, it is very difficult presently to form the parallax barrier such that a slit is arranged to satisfy the minute conditions strictly for such a slit pitch. Even in such circumstances when the slit pitch is uneven, a parallax barrier, is needed for a viewer to observe stereoscopic vision without the sense of incongruity, as disclosed to Japanese Laid-Open Patent Publication No. 08-36145.
In addition, Japanese Laid-Open Patent Publication No. 08-36145 discloses barrier pitch (distance between barriers) rather than slit pitch, but because barrier pitch and slit pitch are equivalent, a similar phenomenon applies to slit pitch as well.
In Japanese Laid-Open Patent Publication No. 08-36145, a barrier is arranged so that a plurality of different barrier pitches (distance between barriers) coexist, and the parallax barrier, which arranged a barrier so that the average of the barrier pitch becomes the ideal barrier pitch, is described. According to such a method, even if a plurality of different barrier pitches coexist and are formed, a parallax barrier allows a viewer a stereoscopic vision without the sense of incongruity by providing the ideal barrier pitch.
However, problems exist in the parallax barrier when different slits are mixed and arranged. In particular, unevenness results by the creation of a gap between each slit and arranged slits in their ideal slit pitch (also referred to here as ideal slit).
Such a problem is specifically explained below. FIG. 3A shows parallax barrier 100 having an ideal slit. In FIG. 3A, the ideal slit pitch is assumed to be 0.099625 mm. The numbers of slits are determined as nine for convenience of explanation.
FIG. 3B shows parallax barrier 110 having a slit arranged with two different slit pitches. In FIG. 3B, one split pitch is 0.100 mm, the other slit pitch is 0.099 nm, and another slit has nine parallax barriers. At this time, (0.100 mm×5+0.099 mm×3)/8=0.099625 mm is obtained, which on average becomes the ideal slit pitch. As described above, when a parallax barrier in FIG. 3B is utilized for stereoscopic visual display device in FIG. 2A, a viewer can have stereoscopic vision without the sense of incongruity. When such barrier is utilized in a multiple visual display device as described in FIG. 2B, each of viewers B and C can observe the different images without a sense of incongruity.
When parallax barriers with a greater number of slits are formed, for example, the combination of the arranged nine slits is deemed one unit (a cycle) for the above average of slit pitch to assume ideal slit pitch, and a parallax barrier is formed in an increase of a slit in every unit. In such a parallax barrier (parallax barrier in a cycle pitch type), the average slit pitch becomes ideal.
FIG. 3C is a diagram showing an overlap between parallax barrier 100 and parallax barrier 110. A hatching area in FIG. 3C shows gap areas with slits on parallax barrier 100 having an ideal slit coexisting with slits on parallax barrier 110 having different slit pitch.
In FIG. 3C, this gap occurs only on the right side or the left side. When the magnitude of this gap area is recognized by the human eye, problems occur. For example, when parallax barrier 110 is utilized for stereoscopic visual display device or multiple visual display devices, hue, chroma, and brightness in images that radiate from each slit differ. This causes a perceptional problem of unevenness to the viewer.